Major thanks, more than I can easily express, go to Linda Regan, executive editor at Prometheus Books, whose wisdom and guidance have been invaluable not only in matters of style but more importantly in matters of content. The subject of evil is problematical and sensitive, arousing strong emotions and inviting acrimonious disagreements. Some question whether a psychiatrist should broach the subject at all. Linda helped me avoid Scylla and Charybdis, keeping me in clear waters. Gratitude, also not easily expressed or measured, goes to Ben Carey of the New York Times, who featured my work on evil in a Science Times article he wrote in February of 2005. His article gave me a presence in this field that granted me access to journalists and to professionals in mental health and law enforcement around the world. Within a few months after the article was published, I was invited to serve as the host of a television program dedicated to educating the public about the often neglected “why” question of evil: What are the forces that prompt persons—civilians in peacetime—to commit the kinds of acts we label as evil? Through the program I had the opportunity to interview some of these men and women. Through these personal contacts it became more clear to me what were the ingredients that underlay the possibility of redemption and what were the ingredients that militated against it.

Even before Ben's article appeared, I had received encouragement to pursue this topic from leaders on psychopathy research: Dr. Robert Hare in Vancouver, and Dr. David Cooke in Glasgow. More recently I shared views and learned a great deal from some of the major writers on violence: Dr. Debra Niehoff and Dr. Katherine Ramsland. A number of prominent writers of true-crime biography gave me information about some of the high-profile murderers about whose crimes, designated evil by the public, I had only scanty knowledge of before. Among these writers: Carol Rothgeb-Stokes, Peter Davidson, Kieran Crowley, and Diane Fanning.

Thanks go to Mary O'Toole of the FBI, who invited me to participate in the First International Congress on Serial Killers, held in San Antonio in 2005. There I became reacquainted with Roy Hazelwood of the FBI, who taught me the fine points about sexual sadism—a topic that overlaps closely with the public's understanding of evil. There are a number of forensic specialists—Dr. Paul Fauteck, Dr. John Hume, and Dr. Norbert Nedopil—to whom I am indebted for more accurate biographical data about some of the persons mentioned in the book.

I owe great thanks to Dr. Charles Smith, former clinical director of the Mid-Hudson Forensic Psychiatric Hospital and my mentor in forensic psychiatry. It was through my work in forensics over the past twenty years that I developed a scale—the Gradations of Evil—by which I have attempted to place evil acts according to the degree of suffering of the victims and to the degree of horror evoked in the public.

As human beings, we are a members of a social species whose survival is threatened now and again by the forces of nature but to a much greater extent through the actions of other human beings. As a result, we have developed a rich vocabulary to depict the subtleties of badness. Our vocabulary for goodness is much skimpier. We do not distinguish between a dozen gradations of honesty, sweetness, amiability, since these qualities merely enhance rather than threaten our survival. But for someone immersing himself in the subject of evil, it is comforting to be surrounded by goodness as a counterbalance to the horror stories I confront daily. It is comforting to be reminded—daily—that there is much more goodness than evil in the world, even though evil is more apt to garner the headlines.

And it is here that my boundless love and gratitude go to my wife, Beth, who—were there a comparable Gradations of Goodness scale—would occupy a spot at its farthest end reserved for the very best of the Good. Beth's virtues are not confined to the spiritual; she read the manuscript as it evolved, made corrections, suggested changes in tone—all that were in line with Linda's recommendations and that contributed to a better manuscript. Better. Not perfect. The imperfections are mine.